Technical Field
The present invention generally relates to a projector having a trapezoidal distortion correction capability, a trapezoidal distortion correction method, and a trapezoidal distortion correction program stored in a storage medium or a carrier medium.
Background Art
Projectors for projecting images have an automatic trapezoidal distortion correction capability or automatic keystone distortion correction capability. When images are projected onto a screen from the projectors, a vertical trapezoidal distortion of the projected image can be detected and the image can be automatically corrected depending on an installation angle of the projectors. The automatic trapezoidal distortion correction capability can be executed by pressing a button.
This type of projector is configured with, for example, a projection unit, a gravity acceleration sensor, and a trapezoidal distortion correction unit. The gravity acceleration sensor detects an installation angle or inclination angle of the projector, the trapezoidal distortion correction unit corrects trapezoidal distortion of the projected image, and the projection unit projects a corrected image onto the screen.
However, with a short throw projector such as an ultra short throw projector having a short focus distance, the inclination angle of the projector affects the projected image quality. For example, when the ultra short throw projector projects an 80-inch image onto a screen from a 400-mm distance while inclined at a 0.3 degree angle, the top of the projected image is about 1794.5 mm long while the bottom of the projected image becomes about 1771.1 mm long. Therefore, the projected image has a trapezoidal distortion corresponding to the difference between the top and bottom lengths, which is 23.4 mm.
The correction performance of the automatic trapezoidal distortion correction capability depends on the resolution level of the gravity acceleration sensor disposed in the projector. For example, a relatively less expensive gravity acceleration sensor has a resolution level of 0.1 degree. But for the ultra short throw projector, a higher resolution level (or a minimum detection angle) is required for the angle detection to project an image within an area of a screen. For example, if the ultra short throw projector inclined 0.3 degree projects an image onto the screen, a higher resolution level such as resolution of 0.1 degree or less is preferable.
Fine adjustment that cannot be conducted automatically can be conducted manually. For example, correction in a range of 0 to 0.3 degree may be conducted manually in steps of, for example, 0.01 degree, which the automatic trapezoidal distortion correction function cannot handle.
In this case, trapezoidal distortion is corrected both automatically and manually, and therefore it is preferable to maintain the corrected condition after manual trapezoidal distortion correction has been conducted.
Further, when the projector is moved, the focus distance and installation angle may change, and the distance and angle change may affect trapezoidal distortion of the projected image. Therefore, it is preferable that automatic trapezoidal distortion correction be conducted once again.
When the projector is moved, resetting of the installation angle by automatic trapezoidal distortion correction can be conducted without pressing a button. Specifically, as disclosed in JP-4831219-B (JP-2010-136327-A), each time the projector is moved, a current automatic trapezoidal distortion correction is cancelled, and then a new automatic trapezoidal distortion correction is automatically conducted. A user is not required to operate the operation button when the projector is moved to enhance user friendliness.
However, for the projector disclosed in JP-4831219-B (JP-2010-136327-A), the trapezoidal distortion correction condition may not be cancelled effectively. For example, when an angular velocity sensor of the projector detects an angular velocity exceeding a threshold value, it is automatically determined that the projector is moved, and the current trapezoidal distortion correction condition is automatically cancelled. Therefore, even if shaking occurred on a desk placing the projector is little and the shaking does not affect a trapezoidal distortion of a projected image, the shaking is detected as a movement of the projector, and the current trapezoidal distortion correction is automatically cancelled and a new trapezoidal distortion correction is automatically conducted again.
As described above, the manual trapezoidal distortion correction may be conducted by a user in addition to the automatic trapezoidal distortion correction of a fine adjustment of trapezoidal distortion correction. If a unnecessary trapezoidal distortion correction is conducted again, the user needs to conduct the manual trapezoidal distortion correction again, which is not user friendly.